Chlorine dioxide (ClO2) may be used in a variety of settings. It is an oxidizing agent that is employed in place of chlorine since it has superior antimicrobial properties and a reduced tendency to produce harmful organic chlorine by-products. Chlorine dioxide is used primarily (>95%) for bleaching of wood pulp, but is also used for pathogen decontamination, water treatment, bleaching of flour and disinfection of municipal drinking water. Its most common use in water treatment is as a pre-oxidant prior to chlorination of drinking water to destroy natural water impurities that produce trihalomethanes on exposure to free chlorine. Trihalomethanes are suspect carcinogenic disinfection byproducts associated with chlorination of naturally occurring organics in the raw water. Chlorine dioxide is also superior to chlorine when operating above pH 7, in the presence of ammonia and amines and/or for the control of biofilms in water distribution systems. Chlorine dioxide is used in many industrial water treatment applications, and as a biocide in cooling towers, water processing and food processing. Chlorine dioxide is less corrosive than chlorine and superior for the control of legionella bacteria.
Chlorine dioxide is also more effective as a disinfectant than chlorine in most circumstances against water borne pathogenic microbes such as viruses, bacteria and protozoa—including cysts of Giardia and the oocysts of Cryptosporidium. 
Chlorine dioxide can also be used for air disinfection, and was the principal agent used for decontamination of buildings in the United States after the 2001 anthrax attacks. Recently, after the disaster of Hurricane Katrina in New Orleans, La. and the surrounding Gulf Coast, chlorine dioxide has been used to eradicate dangerous mold from houses inundated by water from massive flooding. Chlorine dioxide is used as an oxidant for phenol destruction in waste water streams, control of zebra and quagga mussels in water intakes and for odor control in the air scrubbers of animal byproduct (rendering plants). Stablilized chlorine dioxide can also be used in an oral rinse to treat oral disease and malodor.
The industrial preparation of chlorine dioxide is energy-intensive and fraught with health and safety issues. Furthermore, due to the instability of ClO2 at high pressures, the gas is often generated where it is to be used. Large-scale production of ClO2 may involve the use of such reagents as concentrated strong acids and/or externally-added oxidants (such as Cl2, H2O2, or hypochlorite). Electrochemical methods can directly oxidize ClO2− to ClO2 by a 1-electron process but require considerable input of electrical energy and may not be applicable in rural or underdeveloped areas of the world. An iron-catalyzed decomposition of ClO2− has been shown to afford ClO2 (in part), but only under very acidic conditions. Since ClO2 is often generated where it is to be used, these hazardous and/or costly methods must be implemented in facilities that are primarily engineered for other purposes.